The focus of this research program is on the brain bases of individual differences in emotional reactivity. There is great variability among individuals in the nature and intensity of their responses to emotional challenges. These individual differences in emotional reactivity or affective style are related to vulnerability to psychopathology. In the previous grant period, the applicants found that individual differences in baseline electrophysiological measures of activation asymmetry in anterior scalp regions are stable over time, show excellent internal consistency reliability and predict important features of dispositional mood and reactivity to emotion elicitors. Subjects with greater relative left-sided prefrontal activation report more positive and less negative mood and show more intense positive responses to positive emotional film clips. Subjects with relative right-sided prefrontal activation show the opposite profile of mood and emotion. In the next phase of this research program, they will build on the findings and examine the hypothesis that individual differences in prefrontal activation asymmetry primarily reflect the recovery function following an emotional stimulus, or the capacity to terminate an emotion once it has been initiated. The investigators will utilize the emotion-modulated startle paradigm, with startle probes presented both during and after the presentation of an emotional foreground stimulus. They hypothesize that subjects with more relative right-sided prefrontal activation will display greater startle potentiation following both negative and positive emotional stimuli compared with subjects showing more left-sided prefrontal activation. Those with left-sided prefrontal activation are predicted to show more inhibition of startle magnitude following both positive and negative foreground stimuli. In a second experiment, the capacity to voluntarily suppress or enhance emotion will be examined. Subjects with greater left-sided prefrontal activation are predicted to display more facility at suppressing negative emotion compared with those having more right-sided prefrontal activation. Finally, the third experiment will utilize positron emission tomography (PET) to examine individual differences in regional glucose metabolism associated with differences in emotional reactivity as indexed by the emotion-modulated startle task as well as an aversive conditioning task where they will examine the rapidity of extinction of a learned aversive association. Based upon initial data the investigators have collected using PET, they predict that subjects with greater relative right-sided medial prefrontal and amygdala metabolic activity will show slower extinction of an aversive response and poorer recovery of startle following negative stimuli. These data will provide critical new information on the neural substrates of individual differences in affective style and will facilitate the identification of individuals who may be particularly vulnerable to psychopathology.